A procedure for controlling a drive unit is known from U.S. patent application publication 2003/0100405. In this procedure, input quantities, preferably desired torque values for the drive unit from various sources, are coordinated to a resulting desired torque. The drive unit is controlled in dependence upon a desired quantity resulting from these different desired quantities. This known coordination is decentral, that is, the coordination takes place in several independent steps. The resultant of the first stage is the input quantity of the second stage, et cetera. In the embodiment shown, desired quantities, which are independent of the type of drive unit, are coordinated in a first coordinating stage and desired quantities, which are drive unit specific, are coordinated in a second coordination stage. The resultant of the first stage is the input quantity of the second stage.
Here, diverse physical quantities within a motor vehicle are formulated as a request, especially as a torque request to the drive unit. These quantities, for example, include: the driver command; an rpm limitation; a speed limitation; a road speed control; a transmission protection and/or component protection; the intervention of the following: a stability program; a drive slip control; and/or, a drive drag torque control, et cetera. For this reason, the drive unit can be viewed as a component of the vehicle, as an intelligent actuating element for converting such requests. The requests themselves can be assigned to different functional units within the vehicle. Often, these functional units are characterized by their own control apparatus, for example, a stability program or transmission control. This hardware partitioning has, as a rule, grown historically and is therefore not absolutely required.
In present day engine controls, these requests (torque requests), increasing ones as well as decreasing ones, are coordinated in a central function module. An example is shown in DE-A 197 39 567. There, in addition to the torque requests, also all torque limitations are known so that it is ensured that permissible operating limits are not exceeded for engine and total vehicle. Accordingly, an engine desired torque is formed via a targeted sequence of minimum and maximum selection function blocks which does not exceed the permissible operating limits. In a minimum selection block, a minimum selection of the input quantities and therefore a limiting of the torque-reducing interventions takes place; whereas, in a maximum value selection block, a maximum selection of input quantities takes place and therefore increasing interventions are limited.
In the above-mentioned proposal of a partitioning, torque requests are also decentrally evaluated and coordinated via the functional structuring in the vehicle composite. The result of this decentral coordination is then a torque request to the drive unit. Subsequent torque coordinations receive no information as to the source of the torque request. However, if only coordinated desired torques without additional information are transmitted to downstream coordination stages, then the problem arises that a desired torque is pregiven in the downstream coordination which violates the torque limit of a previous coordination.
Accordingly, it is desirable that it is ensured in a decentral torque coordination that no operating limit of a component system and no operating limit of the total system are violated.